Maxim MAX1681ESA, MAX1681C-D, MAX1680C-D, MAX1680ESA Datasheet

_______________General Description

The MAX1680/MAX1681 inductorless switched-capaci­tor voltage converters either invert an input voltage of
+2.0V to +5.5V or double it while supplying up to
125mA output current. They have a selectable-frequen­cy option that allows the use of small capacitors: 4.7µF
(MAX1680), 1µF (MAX1681). With their high output cur­rent capability, these charge-pump devices are suit­able replacements for inductor-based regulators, which
require more expensive external components and addi­tional board space.

The devices’ equivalent output resistance (typically

3.5Ω) allows them to deliver as much as 125mA with
only a 440mV drop. A shutdown feature reduces quies­cent current to less than 1µA. The MAX1680/MAX1681
are available in 8-pin SO packages. For devices that
deliver up to 50mA in smaller µMAX packages, refer to
the MAX860/MAX861 data sheet.

________________________Applications

Local Negative Supplies
Interface Power Supplies
Op-Amp Power Supplies
MOSFET Bias

____________________________Features

♦ Selectable Switching Frequencies:

125kHz/250kHz (MAX1680)
500kHz/1MHz (MAX1681)

♦ Allow Use of Small Capacitors

(1µF for the MAX1681)

♦ 125mA Output Current
♦ 3.5Ω Output Impedance
♦ 1µA Logic-Controlled Shutdown
♦ Configurable as Voltage Inverters or Doublers
♦ +2.0V to +5.5V Input Voltage Range
♦ Available in 8-Pin SO Packages
♦ 90% Efficiency

MAX1680/MAX1681

125mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

________________________________________________________________

Maxim Integrated Products

1

MAX1681

FSEL IN

CAP+ SHDN

GND

C1

1µF

+V

INPUT

+3V TO +5.5V

INVERTED
OUTPUT
VOLTAGE

C2

1µF

1µF

LV

CAP-

INVERTER CONFIGURATION

OUT

MAX1681

FSEL IN

CAP+ SHDN

GND

C1

1µF

C2

1µF

DOUBLED
OUTPUT
VOLTAGE

+V

INPUT

+4V TO +5.5V

NOTE: USE 4.7µF CAPACITORS FOR MAX1680
INPUT VOLTAGE RANGE: +2.5V TO +5.5V.

NOTE: USE 4.7µF CAPACITORS FOR MAX1680
INPUT VOLTAGE RANGE: +2.0V TO +5.5V.

1µF

LV

CAP-

DOUBLER CONFIGURATION

OUT

__________________________________________________Typical Operating Circuits

19-1247; Rev 0; 7/97

PART

MAX1680C/D

MAX1680ESA
MAX1681C/D

0°C to +70°C

-40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*
8 SO
Dice*

______________Ordering Information

*

Contact factory for dice specifications.

Pin Configuration appears at end of data sheet.

MAX1681ESA -40°C to +85°C 8 SO

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone] ext. 3468.

V

MAX1680/MAX1681

125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(

Typical Operating Circuits

(inverter configuration), FSEL = LV = GND, VIN= 5V, C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF

(MAX1681), T

A

= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

IN..............................................................................-0.3V to +6V

LV....................................................(V

OUT

- 0.3V) to (VIN+ 0.3V)

CAP+ ...........................................................-0.3V to (V

IN

+ 0.3V)

SHDN, FSEL ......................................(V

LV

- 0.3V) to (VIN+ 0.3V)

OUT, CAP-..................................................................-6V to 0.3V

Continuous Output Current ..............................................135mA

Output Short-Circuit Duration to GND (Note 1) ...................1sec

Continuous Power Dissipation (T

A

= +70°C)

SO (derate 5.88mW/°C above +70°C)..........................471mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range.............................-65°C to +160°C

Lead Temperature (soldering, 10sec).............................+300°C

I

LOAD

= 125mA

Inverter configuration,
RL= 1kΩ, LV = GND

LV = GND (Note 3)

FSEL = IN or LV
SHDN = IN
OUT = GND, SHDN = IN

CONDITIONS

375 500 625

750 1000 1250

94 125 156

187 250 313

4V

IH

V-3.75 -4.56V

LOAD

Output Voltage Under Load
(Note 2)

V

3.0 5.5

2.0 5.5

V

1V

IL

Shutdown, FSEL Thresholds

µA-1 1I

FSEL

Input Bias Current (FSEL)

Ω3.5 10R

OUT

Output Resistance (Note 2)

Ω1 5R

OUT(SHUT)

Output Resistance to Ground
in Shutdown

µA1I+

SHDN

Shutdown Current

µA-1 1I

SHDN

Input Bias Current (SHDN)

UNITSMIN TYP MAXSYMBOLPARAMETER

Doubler configuration,
RL= 1kΩ, LV = OUT

4.0 5.5

V

IN

2.5 5.5

Input Voltage Range

MAX1680

5.4

mA

10.8

FSEL = IN
(125kHz)

FSEL = LV
(250kHz)

MAX1681

21.6

43.2

I+

FSEL = IN
(500kHz)

Supply Current

FSEL = LV
(1MHz)

Note 1: Shorting OUT to IN may damage the device and should be avoided.

TA= +25°C

TA= +25°C

TA= +25°C

TA= +25°C

MAX1681

MAX1680

MAX1681

MAX1680

TA= +25°C

TA= +25°C

TA= +25°C

TA= +25°C

2.5 4.5

5 9

10 18

20 36

FSEL = LV

157 348

FSEL = IN

MAX1680

79 174

FSEL = LV

570 1490

kHz

FSEL = IN

MAX1681

f

OSC

Switching Frequency

285 745

mA

ELECTRICAL CHARACTERISTICS

(

Typical Operating Circuits

(inverter configuration), FSEL = LV = GND, VIN= 5V, C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF

(MAX1681), T

A

= -40°C to +85°C, unless otherwise noted.) (Note 4)

MAX1680/MAX1681

125mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

_______________________________________________________________________________________ 3

FSEL = IN

FSEL = LV

MAX1681

I

LOAD

= 125mA

21.6

mA

Inverter configuration,
RL= 1kΩ, LV = GND

43.2

Doubler configuration,
R

L

= 1kΩ, LV = OUT

MAX1681

FSEL = LV
FSEL = IN

MAX1680

LV = GND (Note 3)

FSEL = IN or LV
SHDN = IN
OUT = GND, SHDN = IN

CONDITIONS

I+

FSEL = IN
(500kHz)

Supply Current

FSEL = LV
(1MHz)

kHz

285 745

f

OSC

570 1490

79 174

157 348

Switching Frequency

4V

IH

V-3.75V

LOAD

Output Voltage Under Load
(Note 2)

3.0 5.5
V

2.0 5.5

4.0 5.5

V

IN

V

-1 1V

IL

Shutdown, FSEL Thresholds

µA-1 1I

FSEL

Input Bias Current (FSEL)

Ω10R

OUT

Output Resistance (Note 2)

Ω5R

OUT(SHUT)

Output Resistance in
Shutdown

µA1I+

SHDN

Shutdown Current

µA1I

SHDN

Input Bias Current (SHDN)

UNITSMIN TYP MAXSYMBOLPARAMETER

MAX1681

MAX1680

2.5 5.5

Input Voltage Range

MAX1681

MAX1680

MAX1680

5.4

10.8

FSEL = IN
(125kHz)

FSEL = LV
(250kHz)

ELECTRICAL CHARACTERISTICS (continued)

(

Typical Operating Circuits

(inverter configuration), FSEL = LV = GND, VIN= 5V, C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF

(MAX1681), T

A

= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

Note 2: C1 and C2 are low-ESR (<0.2Ω) capacitors. Capacitor ESR adds to the circuit’s output resistance. Using capacitors with

higher ESR reduces output voltage and efficiency. The specified output resistance includes the C1 and C2 0.2Ω ESR.

Note 3: The typical threshold for V

INPUT

other than +5V is 0.35V

INPUT(VIL

= VIH).

Note 4: Specifications to -40°C are guaranteed by design, not production tested.

RL= 100Ω to GND, FSEL = IN

MAX1680
MAX1681

%

80

90

Power Efficiency

UNITSMIN TYP MAXSYMBOLPARAMETER CONDITIONS

MAX1680/MAX1681

125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

4 _______________________________________________________________________________________

__________________________________________Typical Operating Characteristics

(All curves generated using the inverter configuration shown in the

Typical Operating Circuit

s with LV = GND, FSEL = IN or LV,
C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF (MAX1681), and TA= +25°C, unless otherwise noted. Test results are also valid for
the doubler configuration with LV = OUT and TA= +25°C.)

2.5

3.5

5.5

4.5

7.5

6.5

8.5

2.52.0 3.0 3.5 4.0 4.5 5.0 5.5

OUTPUT SOURCE RESISTANCE

vs. SUPPLY VOLTAGE

MAX1680/81TOC04

SUPPLY VOLTAGE (V)

OUTPUT SOURCE RESISTANCE (Ω)

0

1

3

2

5

4

6

-20-40 0 20 40 60 80 100

OUTPUT SOURCE RESISTANCE vs.

TEMPERATURE

MAX1680/81TOC05

TEMPERATURE (°C)

OUTPUT SOURCE RESISTANCE (Ω)

V

INPUT

= 3V

V

INPUT

= 5V

100

0

1 100 1000

MAX1680 EFFICIENCY vs.

LOAD CURRENT (INVERTER CONFIGURATION)

20

40

60

80

MAX1680/81TOC06

LOAD CURRENT (mA)

EFFICIENCY (%)

10

V

INPUT

= 5.5V

V

INPUT

= 4V

V

INPUT

= 3V

FSEL = IN

0

200
100

500
400
300

700
600

800

0 60 8020 40 100 120 140

OUTPUT VOLTAGE DROP

vs. LOAD CURRENT

MAX1680/81TOC01

LOAD CURRENT (mA)

OUTPUT VOLTAGE DROP (mV)

V

INPUT

= 3V

V

INPUT

= 5V

-14

-10

-12

-4

-6

-8

0

-2

2

2.0 3.5 4.02.5 3.0 4.5 5.0 5.5

OSCILLATOR FREQUENCY CHANGE

vs. SUPPLY VOLTAGE

MAX1680/81TOC02

SUPPLY VOLTAGE (V)

OSCILLATOR FREQUENCY CHANGE (%)

MAX1680

MAX1681

-10

-6

-8

-2

-4

2
0

4

8
6

10

-40 0 20-20 40 60 80 100

OSCILLATOR FREQUENCY CHANGE

vs. TEMPERATURE

MAX1680/81TOC03

TEMPERATURE (°C)

OSCILLATOR FREQUENCY CHANGE (%)

MAX1680

MAX1681

MAX1680/MAX1681

125mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

_______________________________________________________________________________________

5

100

0

1 100 1000

MAX1681 EFFICIENCY vs.

LOAD CURRENT (DOUBLER CONFIGURATION)

20

40

60

80

MAX1680/81TOC07

LOAD CURRENT (mA)

EFFICIENCY (%)

10

V

INPUT

= 5.5V

V

INPUT

= 4V

V

INPUT

= 3V

FSEL = IN

1
0

3
2

6
5

4

8
7

9

2.0 3.5 4.02.5 3.0 4.5 5.0 5.5 6.0

MAX1680 SUPPLY CURRENT vs.

SUPPLY VOLTAGE

MAX1680/81TOC08

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

DOUBLER MODE
FSEL = LV

INVERTER MODE
FSEL = IN

INVERTER MODE
FSEL = LV

DOUBLER MODE
FSEL = IN

0

5

15

10

25

20

30

3.02.5 3.5 4.0 4.5 5.0 5.5 6.0

MAX1681 SUPPLY CURRENT vs.

SUPPLY VOLTAGE

MAX1680/81TOC09

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

DOUBLER MODE
FSEL = LV

INVERTER MODE
FSEL = IN

INVERTER MODE
FSEL = LV

DOUBLER MODE
FSEL = IN

3

4

6

5

7

8

9

10

0 4 6 82 10 12 14 1816 20

MAX1680 OUTPUT SOURCE RESISTANCE vs.

CAPACITANCE (INVERTER CONFIGURATION)

MAX1680/81TOC10

CAPACITANCE (µF)

OUTPUT SOURCE RESISTANCE (Ω)

V

INPUT

= 3V, FSEL = LV

V

INPUT

= 5V, FSEL = LV

V

INPUT

= 3V, FSEL = IN

V

INPUT

= 5V, FSEL = IN

3

4

6

5

7

8

9

10

0 4 6 82 10 12 14 1816 20

MAX1681 OUTPUT SOURCE RESISTANCE vs.

CAPACITANCE (DOUBLER CONFIGURATION)

MAX1680/81TOC13

CAPACITANCE (µF)

OUTPUT SOURCE RESISTANCE (Ω)

V

INPUT

= 3V, FSEL = LV

V

INPUT

= 5V, FSEL = LV

V

INPUT

= 5V, FSEL = IN

V

INPUT

= 3V, FSEL = IN

3

4

6

5

7

8

9

10

0 4 6 82 10 12 14 1816 20

MAX1680 OUTPUT SOURCE RESISTANCE vs.

CAPACITANCE (DOUBLER CONFIGURATION)

MAX1680/81TOC11

CAPACITANCE (µF)

OUTPUT SOURCE RESISTANCE (Ω)

V

INPUT

= 3V, FSEL = LV

V

INPUT

= 5V, FSEL = LV

V

INPUT

= 5V, FSEL = IN

V

INPUT

= 3V, FSEL = IN

3

4

6

5

7

8

9

10

0 4 6 82 10 12 14 1816 20

MAX1681 OUTPUT SOURCE RESISTANCE vs.

CAPACITANCE (INVERTER CONFIGURATION)

MAX1680/81TOC12

CAPACITANCE (µF)

OUTPUT SOURCE RESISTANCE (Ω)

V

INPUT

= 3V, FSEL = LV

V

INPUT

= 5V, FSEL = LV

V

INPUT

= 5V, FSEL = IN

V

INPUT

= 3V, FSEL = IN

____________________________Typical Operating Characteristics (continued)

(All curves generated using the inverter configuration shown in the

Typical Operating Circuit

s with LV = GND, FSEL = IN or LV,
C1 = C2 = 10µF (MAX1680), C1 = C2 = 2.2µF (MAX1681), and TA= +25°C, unless otherwise noted. Test results are also valid for
the doubler configuration with LV = OUT and TA= +25°C.)

_______________Detailed Description

The MAX1680/MAX1681 switched-capacitor voltage
converters either invert or double the input voltage.
They have low output resistance (3.5Ω) and can deliver
up to 125mA output current. These devices operate at
one of two selectable frequencies: 125kHz/250kHz
(MAX1680) and 500kHz/1MHz (MAX1681). This pro­vides the flexibility to optimize capacitor size, operating
supply current, and overall circuit efficiency. Frequency
selection also allows for minimizing coupling into other
sensitive circuits. These devices contain no internal
divider; the oscillator frequency equals the switching
frequency. The devices can easily be cascaded to pro­duce a higher output voltage, or paralleled to deliver
more current.

The MAX1680/MAX1681 feature a shutdown mode that
reduces supply current to <1µA (SHDN = high). OUT,
in the inverter configuration, pulls to ground in shut­down mode. Shutdown is not available in the doubler
configuration; connect SHDN to OUT.

__________Applications Information

Voltage Inverter

A simple voltage inverter is the most common
MAX1680/MAX1681 application. It requires three exter­nal capacitors (including the input bypass capacitor)
as shown in the

Typical Operating Circuits

(inverter

configuration). Although the output is not regulated, low

output resistance produces a typical drop of only 0.44V
with a 125mA load. This low output resistance makes
the devices fairly insensitive to changes in load (see
the graphs for Output Source Resistance vs.
Temperature and Supply Voltage in the

Typical

Operating Characteristics

section).

Voltage Doubler

The MAX1680/MAX1681 can be configured as a volt­age doubler with two external capacitors as shown in
the

Typical Operating Circuits

(doubler configuration).
When loaded, the output voltage drop is similar to that
of the voltage inverter. The minimum input supply range
is slightly higher than in the inverter configuration.
Calculate ripple voltage using the equation in the

Capacitor Selection

section.

Frequency Control

A frequency-control pin, FSEL, provides design flexibili­ty. Each device has two selectable frequencies:
125kHz/250kHz (MAX1680) and 500kHz/1MHz
(MAX1681). This allows optimization of capacitor size
and supply current for a given output load. Table 1
summarizes the frequency options .

Table 1. Nominal Switching Frequencies

MAX1680/MAX1681

125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

6 _______________________________________________________________________________________

______________________________________________________________Pin Description

Selects operating frequency. MAX1680: 250kHz when FSEL is low, 125kHz when FSEL is high. MAX1681:
1MHz when FSEL is low, 500kHz when FSEL is high.

FSEL1

Positive Charge-Pump Capacitor ConnectionCAP+2

Negative Charge-Pump Capacitor ConnectionCAP-4

Power-Supply Ground InputGND3

Logic Voltage Input. Connect LV to GND.LV6

Power-Supply Positive Voltage InputIN8

SHDN7

Negative Voltage OutputOUT5

Power-Supply Positive Voltage Input

Power-Supply Ground Connection
Connect LV to OUT.

Not available; connect to OUT.

Shutdown Input. Driving SHDN high disables the
charge pump, and the output goes to 0V. SHDN is a
CMOS input.

Positive Voltage Output

MAX1680

250FSEL = LV
125FSEL = IN

FSEL CONNECTION

MAX1681

1000

500

FREQUENCY (kHz)

INVERTER DOUBLER

PIN

FUNCTION

NAME

Operating Frequency Trade-Offs

It is important to recognize the trade-offs between
switching frequency, power consumption, noise, cost,
and performance. Higher frequency switching reduces
capacitor size while maintaining the same output
impedance, thus saving capacitor cost and board
space. Lower frequency designs use less supply cur­rent. Table 2 summarizes the relative trade-offs.

Table 2. Switching-Frequency Trade-Offs

Capacitor Selection

The MAX1680/MAX1681 are tested with capacitor val­ues of 10µF and 2.2µF, respectively. Capacitor size
and switching speed determine output resistance.
Larger C1 values decrease the output resistance until
the internal switch resistance (3.5Ω typ) becomes the
dominant term. Low-ESR capacitors minimize output
resistance and ripple voltage. The entire circuit’s output
resistance can be approximated by the following equa­tion:

R

OUT

≅ RO+ 4 x ESRC1+ ESRC2+ [1 / (f

OSC

x C1)] +

[1 / (f

OSC

x C2)]

where ROis the device’s internal effective switch resis­tance and f

OSC

is the switching frequency. Output

resistance is a critical circuit component, as it deter­mines the voltage drop that will occur at the output from
the ideal value of -V

INPUT

(or 2V

INPUT

when doubling).

To optimize performance, minimize overall resistance in
the system. In particular, equivalent series resistance
(ESR) in the capacitors produces significant losses as
large currents flow through them. Therefore, choose a
low-ESR capacitor for highest efficiency. Table 3 lists
recommended capacitors and their suppliers.

Calculate the output ripple voltage as follows:
V

RIPPLE

= [(I

OUT

) / (2 x f

OSC

x C2)] + 2 x (I

OUT

x ESRC2)

where I

OUT

is the load current, fSis the charge pump’s
operating frequency, C2 is the output capacitor, and
ESRC2is the output capacitor’s ESR.

Table 4 lists the minimum recommended capacitances
that allow for the maximum output current. The output
capacitor, C2, is normally equal to or greater than the
charge-pump capacitor, C1. Capacitor values can be
scaled directly proportional to the input voltage, fre­quency, and load current. For example, for V

INPUT

=

5V, I

LOAD

= 125mA at f

OSC

= 125kHz, a 6.4µF mini-

mum capacitor is recommended. For an output of only

62.5mA, a 3.2µF capacitor is recommended. C1’s value
can be estimated as follows:

C1 = 6.4µF x (V

INPUT

/ 5.0V) x (125kHz / f

OSC

) x

(I

LOAD

/ 125mA)

where f

OSC

is the switching frequency (kHz) and I

LOAD

is the output current (mA) required.

MAX1680/MAX1681

125mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

_______________________________________________________________________________________ 7

ATTRIBUTE

C1, C2 Values Larger

LOWER

FREQUENCY

Output Ripple Larger

Smaller

Smaller

SUPPLIER

Marcon/United Chemi-Con [phone]

PHONE

AVX

[phone]
[phone]

[phone]

[phone]

HIGHER

FREQUENCY

Supply Current Smaller Larger

FAX DEVICE TYPE

Ceramic capacitors

Surface mount, TPS series

Matsuo [phone] [phone] Surface mount, 267 series
Nichicon

USA: [phone]
Japan: 81-7-5231-8461

USA: [phone]
Japan: 81-7-5256-4158

Sanyo

USA: [phone]
Japan: 81-7-2070-6306

USA: [phone]
Japan: 81-7-2070-1174

Through-hole, OS-CON series

Through-hole, PL series

Sprague [phone] [phone]
TDK [phone] [phone] Ceramic capacitors

Surface mount, 595D series

United Chemi-Con [phone] [phone]
Vishay/Vitramon [phone] [phone] SMT ceramic chip capacitors

Through-hole, LXF series

Table 3. Low-ESR Capacitor Suppliers

MAX1680/MAX1681

Bypass Capacitor

Bypass the input voltage to reduce AC impedance and
to prevent internal switching noise. Bypassing depends
on the source impedance location. The AC ripple cur­rent is 2 x I

OUT

for the doubler and the inverter. Use a
large bypass capacitor (equal to C1) if the supply has
high AC impedance.

Cascading Devices

To produce larger negative voltages, cascade two
devices (Figure 1). For two devices, the unloaded out­put voltage is approximately -2 x V

INPUT

, but this value
is reduced slightly by the first device’s output resis­tance multiplied by the second device’s quiescent cur­rent. The effective output resistance for a cascaded

device is larger than that for an individual device (20Ω
for two devices). Cascading several devices increases
output resistance and reduces efficiency. If a large
negative voltage is required for several stages, an
inductive inverting switching regulator such as the
MAX629 or MAX774 may offer more advantages.

Paralleling Devices

Parallel two or more MAX1680/MAX1681s to reduce
output resistance voltage drop under a given load. With
reduced output resistance, paralleled devices deliver
higher load currents. Figure 2 shows two
MAX1680/MAX1681s connected in parallel. Output
resistance is inversely proportional to the number of
devices.

125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

8 _______________________________________________________________________________________

250 1.2

125 2.5

1.9

3.8

500 0.6 0.9

Table 4. Minimum Recommended Capacitances for Maximum Output Current

CAPACITANCE (µF) (C1 = C2)

2.5

5.1

3.2

6.4

1.2 1.6

1000 0.3 0.4 0.6 0.8

VIN= 3V

f

OSC

(kHz)

VIN= 2V VIN= 5VVIN= 4V

MAX1681

FSEL IN
CAP+ SHDN

GND

1µF

1µF

1µF

LV

CAP- OUT

MAX1681

FSEL IN
CAP+ SHDN

GND

+V

INPUT

V

OUT

= -V

INPUT

1µF

NOTE: USE 4.7µF CAPACITORS FOR MAX1680.

1µF

LV

CAP- OUT

V

OUT

= -2V

INPUT

Figure 1. Cascading MAX1680/MAX1681s to Increase Output Voltage

Combined Doubler and Inverter

Figure 3 shows a single MAX1680/MAX1681 as an
inverter and a doubler. The maximum output current is
the sum of the loads on the two outputs and is still limit­ed to 125mA. As the device is loaded, the output volt­ages move toward ground. In this particular
configuration, connect LV to GND (inverter). The diodes
used in the circuit cause a drop of approximately 0.7V
in the doubler’s output voltage, impacting efficiency.

Compatibility with the MAX660 and

MAX860/MAX861

The MAX1680/MAX1681 can be used in place of the
MAX860/MAX861, except for the SHDN and FSEL pins.
The MAX1680/MAX1681 shut down with a high input
voltage, compared with the MAX860/MAX861. The
MAX1680/MAX1681 have only two frequency choices.

Replacing the MAX660 with the MAX1680/MAX1681
involves a wiring change, as the external oscillator pin
is replaced by the shutdown feature. Table 5 compares
the devices.

MAX1680/MAX1681

125mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

_______________________________________________________________________________________ 9

MAX1681

FSEL IN

+V

INPUT

CAP+ SHDN

GND

1µF

1µF

LV

CAP- OUT

GND

MAX1681

"n"

FSEL IN

CAP+ SHDN

1µF

1µF

1µF

V

OUT

NOTE: USE 4.7µF CAPACITORS FOR MAX1680. V

OUT

= -V

INPUT

LV

CAP- OUT

R

OUT

=

R

OUT

OF SINGLE DEVICE

NUMBER OF DEVICES (n)

Figure 2. Paralleling MAX1680/MAX1681s to Increase Output Current

MAX1681

FSEL IN

+V

INPUT

CAP+ SHDN

GND1µF

1µF

1µF

1µF

1µF

LV

CAP- OUT

V

OUT

= -V

INPUT

D1
IN4148

D2

IN4148

V

OUT

= 2V

INPUT

-V

FD1

-VFD2

NOTE: USE 4.7µF CAPACITORS FOR MAX1680.

Figure 3. Combined Doubler and Inverter

MAX1680/MAX1681

125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

10 ______________________________________________________________________________________

LV

OUTCAP-

1
2

87IN

SHDNCAP+

GND

FSEL

SO

TOP VIEW

3

4

6

5

MAX1680
MAX1681

__________________Pin Configuration ___________________Chip Information

TRANSISTOR COUNT: 171
SUBSTRATE CONNECTED TO IN

OUTPUT

CURRENT

(mA)

PART NUMBER

MAX665 0.20/1.0

TYPICAL

QUIESCENT

CURRENT (mA)

MAX660 0.12/1.0

100

100

MAX860 0.20/0.60/1.40 50

SWITCHING

FREQUENCY

(kHz)

6.5

OUTPUT

RESISTANCE

(Ω)

6.5
5/40

5/40

12 6/50/130

MAX1680 2.5/5.0

MAX861 0.30/1.10/2.50

125

50

MAX1681 10/20 125

3.5

12

125/250

13/100/250

3.5 500/1000

ICL7660 0.080 10 55 5

Table 5. Device Comparison

MAX1680/MAX1681

125mA, Frequency-Selectable,

Switched-Capacitor Voltage Converters

______________________________________________________________________________________ 11

________________________________________________________Package Information

SOICN.EPS

MAX1680/MAX1681

125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters

NOTES

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

12

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